The luminosity associated with the combustion of aviation turbine fuels can have a significant impact on the performance and long term durability of jet aircraft engines. Radiative heat transfer to the combustor liner walls increases with increasing luminosity, leading to higher wall temperatures and ultimately to reduced combustor lifetimes due to loss of structural integrity. Flame luminosity is also related to the amount of soot formed from the fuel, an important consideration for exhaust smoke emissions.
Standardized fuel quality specifications have been developed in an attempt to consistently insure proper combustion characteristics related to flame luminosity and soot formation. These specifications are based on ASTM test methods and include smoke point tests (D 1322) and luminometer number test (D 1740). However, because these testing procedures are conducted under conditions far different from those in real engine combustors, it has often been difficult to correlate these results with the engine performances. As a result, some engine combustors have been modified and instrumented to measure the flame luminosity and its effect on the liner temperatures as a function of fuel type. Good results can be obtained from such experiments; there are, however, several drawbacks to this approach:
1. The results are highly sensitive to the particular model of the combustor used because of the uniqueness of the design, such as spray, cooling method and physical configuration.
2. These combustor test rigs are complex and are expensive to construct and operate. The large fuel samples required often exceed the volume of the experimental fuels available.